1. Field of the Invention
The present invention relates to a speckle interferometer apparatus for measuring deformations by using electronic speckle interferometry. In particular, the present invention relates to a speckle interferometer apparatus which takes account of convenience of exchanging image pickup cameras and the like when capturing interference speckle pattern images concerning temporal deformations (in-plane deformations in particular) of dynamic objects.
2. Description of the Prior Art
Conventionally, deformation measuring methods using electric strain gauges have widely been used for observing processes in which objects bearing a load deform and collapse. Known on the other hand is speckle interferometry which can carry out highly accurate deformation measurement with reference to wavelengths of light in a two-dimensional field of view with respect to deformations of an object.
The speckle interferometry is interferometry utilizing speckle-like patterns (speckle patterns) occurring in an observation surface when a rough object is irradiated with laser light. Speckle patterns are considered as image noises which are unfavorable in typical image-forming systems. However, they carry surface information of the rough object, whereby deformations can be estimated from changes in the speckle patterns. It is also advantageous in that the surface of the rough object can be observed without any particular preprocessing, thus requiring no photoplate with a high resolution or the like which is necessary for holography.
With reference to FIG. 8, a conventional speckle interferometer apparatus 502 of dual luminous flux irradiation type will be explained. An object 501 to be observed, which is a rough object, is irradiated with a laser luminous flux from a laser light source 701 (only the luminous flux exit position thereof being depicted) disposed substantially symmetrical to the object 501 within an xz plane (plane parallel to the paper surface). The laser luminous flux outputted from the laser light source 701 reaches a beam splitter 705b by way of a collimator 612 and a reflecting mirror 705a. One of the laser luminous fluxes divided by the beam splitter 705b travels reflecting mirrors 705c, 705d and a concave lens 602a, and is reflected by a reflecting mirror 601a so as to illuminate the object 501. The other travels reflecting mirrors 705e, 705f, 705g and a concave lens 602b, and is reflected by a reflecting mirror 601b so as to illuminate the object 501. The two luminous fluxes are configured so as to yield a predetermined optical path length difference for convenience of phase analysis processing of interference speckle pattern images. The two luminous fluxes thus illuminating the object 501 are divergently reflected thereby, so as to form an interference speckle pattern on an image-forming surface of a CCD camera 503. Thereafter, thus obtained interference speckle pattern image is analyzed, so as to carry out a phase analysis in conformity to the surface form of the object 501.
Known in the phase analysis of interference speckle pattern images is a technique in which interference speckle patterns of the object 501 before and after a deformation are captured, and the difference in intensity is calculated for each image point.
Two shutters are placed on respective optical paths of the divided luminous fluxes, and intensity distributions I1(x; t), I2(x; t) for the individual image points in a time domain obtained when the object is irradiated with one luminous flux alone are measured before the phase analysis.
In general, an interference pattern I(x; t) obtained in an optical system of a speckle interferometer apparatus is represented by the following expression (1):I(x;t)=I0(x;t)[1+γ(x;t)cos(θ(x;t)+φ(x;t))]  (1)where I0(x; t) is the average intensity of I1(x; t) and I2(x; t), θ(x; t) is a random speckle phase, γ(x; t) is the degree of modulation, and φ(x; t) is the object phase.
In the conventional speckle interferometer apparatus such as the one mentioned above, two irradiation optical systems for irradiating the object 501 with luminous fluxes from the laser light source 701 and the CCD camera 503 for capturing an image of interference speckle patterns are accommodated together in the apparatus.
For measuring dynamic interference speckle patterns, there has been a demand for exchanging the CCD camera 503 between a normal CCD camera and a high-speed camera or among various high-speed cameras according to the rate of deformation of the object 501 or the like. In such a case, the housing of the apparatus and its inner mechanical parts must be disassembled for exchanging the cameras in the above-mentioned apparatus.